The present invention relates to a metallic eyeglass frame of the type having a shape-memory effect and a method of the making the same.
In general, an eyeglass frame is composed of several members, such as an eyeglass rim, a bridge, and a temple. A pair of eyeglass rims are connected to each other by the intervention of one or more bridges. The bridge is provided at the both ends with a couple of pad-holders each holding a pad. Each rim is provided at its outside with a rim lock connected to a temple by the use of a hinge and a screw. The members are made of many sorts of materials, such as metal and plastics. Above all, metallic eyeglass frames are most popular because of being superior in use, easy for design and fashionable in appearance. The conventional members have been made from metallic materials containing one or more of Cu-Ni-Zn alloy(nickel silver), Ni-Cr alloy, titan and/or stainless steel.
Recently, a superelastic Ni-Ti base alloy has been proposed as a metallic material for use in fabricating the member of an eyeglass frame because of being elastically formable to a remarkable extent in comparison with the conventional metallic material. Therefore, it is expected that the Ni-Ti base alloy, if used as a material to form an eyeglass frame, may improve such properties of the frame as shape-keeping, recovery from deformation, and mutual connection between the members and fitness to the user's face.
However, the Ni-Ti base alloy is relatively poor in machinability, so that it should be limited to a member that is simple in shape and necessary for it to have a shape-memory effect and the other members rather than being made from the usual metallic material. This means that the Ni-Ti base alloy member is always bonded to the other member. The bonded portion in the eyeglass frame is required to have a high tensile strength as well as a shearing strength more than 15 kg/sq.mm because of subjection to tension, torsion and peeling. The shearing strength more than 15 kg/sq.mm can be obtained if the same Ni-Ti base alloy members are joined with each other by spot-welding. But, the spot-welding is unavailable for joining the tiny members of the eyeglass frame. The spot-welding apparatus is too large to be used for joining the members. Besides, the spot-welding can not be achieved without a spot of welding remaining which surely causes damage in appearance of the frame. The Ni-Ti base alloy member is joined with the other member by soldering. However, no strong bonding is obtained by soldering between two members of which either contains the Ni-Ti base alloy. The reason for this is that solder is not easy to flow over nor solid-solved in the intermetallic compound of the Ni-Ti alloy even if soldering is made under the atmosphere of argon gas. The soldered portion no more than connects the Ni-Ti base alloy member with the other member, having a strength much less than 15 kg/sq.mm.